1. Technical Field Of The Invention
The present invention relates to a liquid crystal display and a method for producing the same.
2. Prior Art
Conventionally, a COG (chip-on-glass) module and a COF (chip-on-film) module have been publicly known as liquid crystal displays.
FIG. 11 shows a configuration of a COG module (wherein FIG. 11(a) is a plan view and FIG. 11(b) is a view taken along the line Axe2x80x94A of FIG. 11(a)). The COG module shown in FIG. 11 is composed of a liquid crystal displaying portion 43 that is obtained by overlapping a surface substrate 41 and a rear substrate 42, to each of which conductive line (not illustrated) constituting a transparent pixel electrode 45 is applied, and sealing liquid crystal in pixel areas sectioned by sealing agents between the corresponding substrates 41 and 42; and a circuit substrate portion 47 in which an LSI (IC) 46 connected electrically to the above-described transparent pixel electrode 45 is connected to an area in which terminals of the above-described transparent pixel electrodes 45 is provided on the surface substrate 41 or the rear substrate 42, and a plurality of conductive lines of these transparent electrode 45 are integrated.
Transparent resin and transparent glass are used as the above-described surface and rear substrates 41 and 42. However, since, in many cases, glass is employed, areas to which the LSI 46 is connected are provided on a glass substrate. Therefore, there may be cases where a liquid crystal display consisting of the above liquid crystal displaying portion 43 and circuit substrate portion 47 is called a xe2x80x9cchip-on-glassxe2x80x9d module.
The COG module employs a flexible cable such as FPC 49 as a cable for connection from a conductive line of the LSI 46 to the power source (not illustrated) side.
Also, the liquid crystal display in which the COF is used is shown in FIG. 12 (wherein FIG. 12(a) is a plan view, and FIG. 12(b) is a sectional view taken along the line Axe2x80x94A in FIG. 12(a)). The COF module is composed of a liquid crystal displaying portion 53 in which a surface substrate 51 and a rear substrate 52 having conductive line, which constitutes a transparent electrode, applied thereto are, respectively, overlapped with each other, and liquid crystal is poured and sealed in pixel areas sectioned by a sealing agent between both of the corresponding substrates 51 and 52; and a circuit substrate portion 59 that forms conductive lines 55 of metallic copper, connected to conductive lines from the corresponding liquid crystal displaying portion 53, on a circuit substrate 57 made of synthetic resin film such as expensive polyimide resin, etc., and connects an LSI (IC) 56, which is connected electrically to the transparent pixel electrode of said liquid crystal displaying portion 53, to an area in which the above-described conductive lines 55 of metallic copper are integrated.
The conductive lines of the LSI (IC) 56 on the above-described circuit substrate portion 59 are configured so as to be connected to the power source side via an anisotropic conductive film (not illustrated), etc. However, in the configuration shown in FIG. 12, since the LSI 56 is provided on a synthetic resin film, the same may be called a xe2x80x9cchip-on-filmxe2x80x9d module.
In the liquid crystal display constructed as shown in FIG. 12, the LSI (IC) 56 is connected to the conductive lines in the order shown in FIG. 13. First, as shown in FIG. 13(a), a copper foil 60 is adhered to the surface of the circuit substrate 57 (FIG. 13(b)), the same is etched after a masking agent 63 is coated (FIG. 13(c)), and a pattern of copper conductive lines 55 is formed. Next, an ACF (Anisotropic Conductive Film) 58 is adhered to the pattern of the etched copper conductive lines 55 (FIG. 13( )), and the LSI (IC) 56 is thermally pressure-fitted from above the ACF 58 (FIG. 13(f)).
In the configuration of the COG module shown in FIG. 11, since the liquid crystal displaying portion 43 and the circuit substrate portion 47 are provided on the rear substrates 41 and 42, the area of the circuit substrate portion 47 in which the LSI 46 of the COG module is mounted is increased, the area occupied by the circuit substrate portion 47 is increased in comparison with the liquid crystal displaying portion 43 that brings about its inherent features and functions as a liquid crystal display. Since the FPC 49 that is a flexible cable is disposed on the surface of the rear substrate 42, the flexible property of the FPC 49 cannot be completely displayed, and since the circuit substrate portion (LSI-mounted part) 47 is provided on a glass substrate together with the liquid crystal displaying portion 43, it is not possible to fold the circuit substrate portion 47.
Also, in the configuration of the COF module, which is shown in FIG. 12, in order to form conductive lines 55, having a minute thickness, of non-transparent copper on the circuit substrate 57 made of polyimide resin film being a flexible film as shown in FIG. 13, the cost of producing a mask to form conductive lines, and the cost for inspection of connecting electrically to the conductive lines after the conductive lines are formed are incidentally increased. In addition, since polyimide resin is expensive, and the product cost will be accordingly increased, which cannot be ignored as a problem.
Further, the circuit substrate 57 that is composed of copper conductive lines 55 and a polyimide resin film is non-transparent as shown in FIG. 13(f), and there is a shortcoming by which the connected state between the copper conductive lines 55 and LSI 56 cannot be visibly confirmed.
Thus, since the COF module employs a number of production steps and uses expensive materials, there are many cases where the development costs cannot be depreciated in a case of producing custom products in a small lot.
Also, in the COF module shown in FIG. 12, it is necessary to prepare a photo mask to produce a circuit substrate portion 57 for connection of the LSI 56, a metal mold for cutting the outer profile thereof, and special tools and fixtures to fix a soft polyimide resin film, and high initial costs are required. Also, since expensive ultra-thin polyimide films and ultra-thin copper foils 60 are used as the materials of the circuit substrate 57, the unit price thereof is very expensive. In addition, since the circuit substrate materials and circuit conductive lines are not transparent, it is not possible to visibly check the connected state of the LSI 56 when it is mounted on the circuit substrate portion 57.
Therefore, it is an object of the present invention to provide a liquid crystal display that employs the COG technology, is able to mount LSIs in a narrow space and, after the LSIs are mounted, to visibly check the mounted state (that is, its electrically connected state) and the lighting of a picture displaying portion, and a method for producing the same. Also, it is another object of the invention to provide a liquid crystal display that has high reliability and whose production cost is lower, and a method for producing the same.
These objects of the invention can be achieved and solved by the following configurations (1) and (2):
(1) A liquid crystal display comprising: a liquid crystal displaying portion in which a first substrate having a transparent pixel electrode provided thereon and a second substrate having a transparent opposed pixel electrode provided thereon overlaps each other so that both the above-described electrodes are disposed so as to be opposed to each other, and liquid crystal is sealed in a pixel area between the above-described first substrate and the above-described second substrate; a hard transparent substrate having a transparent conductive electrode provided thereon; a circuit substrate portion that is mounted on the surface of the above-described hard transparent substrate and is provided with integrated circuit chips connected electrically to the above-described transparent conductive electrode; and flexible connecting means for electrically connecting the transparent pixel electrode of the above-described liquid crystal displaying portion with the transparent conductive electrode of the above-described circuit substrate portion.
In the liquid crystal display of the COF module type, which is a prior art and is shown in FIG. 12, the LSI 56 is bonded to the circuit substrate 57 made of non-transparent polyimide resin film. However, according to the above-described invention, integrated circuit chips are bonded on a hard transparent substrate, which is a hard material. Thus, since the integrated circuit chips are bonded on a hard substrate, work can be facilitated, and, in comparison with bonding of integrated circuit chips on a non-transparent film as in the prior arts, it is possible to visibly check the bonding conditions of the integrated circuit chips from the surface of the hard transparent substrate at the side where no integrated circuit chip of the transparent substrate is mounted. Therefore, no expensive checking apparatus is required, and this is advantageous.
In addition, in comparison with the COF module type in FIG. 12, it is possible to produce liquid crystal displays at a low cost since the liquid crystal displays according to the invention do not use any expensive polyimide resin.
Also, since the liquid crystal displaying portion and the circuit substrate portion of the above-described liquid crystal display according to the invention can be disposed so that the middle portion of the flexible connecting means is folded over, the liquid crystal display can be made compact.
In comparison with a liquid crystal display of COG module type, which is shown in FIG. 11 and belongs to the prior arts, since the circuit substrate portion can be folded over in the above-composed liquid crystal display according to the invention, the area occupied by the liquid crystal displaying portion in the entire liquid crystal display can be increased.
Also, in the above-described liquid crystal display according to the invention, it is preferable that the surface on which integrated circuit chips of the above-described circuit substrate portion are mounted is disposed at the position opposite to the above-described liquid crystal displaying portion.
Where the surface on which integrated circuit chips of the above-described circuit substrate portion are mounted is disposed at the position opposite to the above-described liquid crystal displaying portion, since the integrated circuit chips are not exposed from the substrate surface, it is possible to prevent the integrated circuit chips from being influenced by an external impact when a liquid crystal display is set in a casing.
Further, any one of a flexible printed circuit (FPC), a heat seal, a flexible flat cable (FFC), and an anisotropic conductive rubber connector may be used as the above-described flexible connecting means of the invention.
By connecting the liquid crystal displaying portion and circuit element portion to each other via the flexible connecting means, and causing the flexible connecting means to be folded over, the liquid crystal display portion and circuit element portion are caused to overlap each other, wherein a space-saving liquid crystal display can be obtained.
The first substrate, second substrate and hard transparent substrate of the above-described liquid crystal display according to the invention may be made of a transparent glass plate or transparent synthetic resin plate.
At this time, since the plate thicknesses of the first and second substrates and the hard transparent substrate are made the same, it is possible to obtain a number of the above-described three substrates from a single transparent plate having a large area, wherein the productivity thereof is made higher than in the case where the above respective substrates are separately produced.
Also, it is highly recommended that an infrared ray shielding film be coated onto the surface of the hard transparent substrate other than the portion where the above-described integrated circuit chips are mounted. With the construction, it is advantageous in that a liquid crystal display (for example, of a portable device), which is used outdoors and may be exposed to sunlight does not erroneously operate.
(2) A method for producing a liquid crystal display in which a first substrate having a transparent pixel electrode provided thereon and having a sealing agent, which sections the pixel area, coated thereon, and a second substrate having a transparent opposed pixel electrode provided thereon are disposed so that both the above-described electrodes face each other, and liquid crystal is sealed in respective pixel areas between the above-described first substrate and the above-described second substrate to make the same into a liquid crystal portion; integrated circuit chips connected electrically to a transparent conductive electrode are mounted on the surface of the hard transparent substrate having the above-described transparent conductive electrode provided thereon to make the same into a circuit substrate portion; and the transparent conductive electrode of the above-described circuit substrate portion and the transparent pixel electrode of the above-described liquid crystal displaying portion are electrically connected to each other by flexible connecting means; comprising the steps of: producing a single transparent substrate having a large area, which is constructed of a plurality of sets disposed in one or more rows each set consisting of the above-described first substrate portion, the above-described hard transparent substrate portion and the above-described second substrate portion arrayed in this order; overlapping the first substrate portion, hard transparent substrate portion and second substrate portion of the above-described respective sets so as to be disposed in the opposite direction, using two of the above-described transparent substrates having a large area; forming a liquid crystal displaying portion area having a liquid crystal-sealed space, which is composed of the first substrate portion, the second substrate portion and a sealing agent, formed therein, the above-described liquid crystal displaying portion being disposed at the position where the above-described overlapped two transparent substrates having a large area are faced to each other; forming a circuit substrate portion area in which integrated circuit chips are mounted on the hard transparent substrate portion adjacent to the above-described liquid crystal displaying portion area; and acquiring a plurality of units for producing a liquid crystal display by cutting and separating the above-described two transparent substrates having a large area, in which a plurality of units for producing a liquid crystal display, consisting of the above-described acquired liquid crystal displaying portion area and the above-described circuit substrate portion area are arrayed.
In the above-described method for producing a liquid crystal display, the above-described step for cutting and separating two overlapped transparent substrates having a large area may further comprise the step of primarily cutting and separating the above-described plurality of units for producing liquid crystal displays row by row, each row having a plurality of units, respectively, and secondarily cutting and separating one row, which is cut and separated by the above-described primary cutting and separating step, unit by unit, each unit being for producing respective liquid crystal displays.
Also, liquid crystal may be poured and sealed in respective liquid crystal displaying portion areas in a plurality of units for producing liquid crystal displays in the respective rows in order to obtain liquid crystal displaying portions after the above-described primary cutting and separating step, and the above-described secondary cutting and separating step may be carried out thereafter.
In addition, integrated circuit chips connected electrically to the transparent conductive electrodes are mounted on the surface of the hard transparent substrate after the above-described secondary cutting and separating step, thereby making the same into a circuit substrate portion.
Still further, the liquid crystal displaying portion of the respective units for producing liquid crystal displays, which is provided with a circuit substrate portion incorporating integrated circuit chips after the above-described secondary cutting and separating step and the circuit substrate portion may be cut and separated from each other, and thereafter, the conductive end portions from respective electrodes of the corresponding liquid crystal portion and circuit substrate portion may be electrically connected to each other by a flexible connecting means to obtain a liquid crystal display, whereby the liquid crystal displaying portion and the circuit substrate portion may be disposed after they are folded over via the flexible connection means and overlapped with each other.
There are three types of shapes of transparent electrodes in the liquid crystal display according to the invention. However, with the method for producing the liquid crystal display according to the invention, it is possible to produce these transparent electrodes through a single process of photolithography by using a single masking substrate. That is, in the prior art method, one or two masks are required for the first and second substrates for a liquid crystal displaying portion, and one mask that is necessary for a circuit substrate portion is required, wherein two or three masks are requisite in all. However, in the present invention, using a single transparent substrate having a large area, the above-described three types of transparent electrodes can be formed at one time, wherein only a single mask is required. Therefore, the exposure process and patterning process can be reduced to half or less. In addition, where the liquid crystal display portion area and circuit element portion area are produced with a single transparent substrate (glass, etc.), the circuit element portion can be produced in the same process order simultaneously as in the process of producing a liquid crystal displaying portion immediately before mounting the integrated chips of the circuit element portion.
Also, the liquid crystal displaying portion area and circuit element portion area are simultaneously produced in the same process order by using two transparent substrates having a large transparent substrate. After that, since the primary cutting and separating step for cutting and separating respective rows including a plurality of units for producing liquid crystal displays in a line is carried out, and a plurality of units for producing liquid crystal displays can be obtained at one time after the primary cutting and separating process, the productivity of the liquid crystal displays can be increased.
Also, where liquid crystal is sealed in a plurality of units for producing liquid crystal displays after the above-described primary cutting and separating process, it is possible to seal liquid crystal in a number of the above-described units with a single operation, wherein work efficiency can be increased.
Also, since it is possible to bond integrated circuit chips onto hard transparent substrates of a plurality of units for producing liquid crystal displays after the above-described secondary cutting and separating step, and it is possible to easily and securely inspect the electrical connections to the transparent conductive electrodes on the hard transparent substrates of integrated circuit chips, and it is possible to simultaneously check the lighting of a plurality of liquid crystal display units of the integrated circuit chips.
Therefore, according to the liquid crystal display of the invention, since the LSI-mounted portion can be disposed on the rear side of the liquid crystal displaying portion where the circuit substrate portion is connected to the liquid crystal displaying portion by a flexible connecting means, a compact liquid crystal display can be obtained.
Also, according to the method for producing a liquid crystal display of the invention, a plurality of sets of a liquid crystal displaying portion area and a circuit substrate portion area can be produced from a single transparent substrate having a large area, and three types of transparent conductive lines can be produced with a single masking substrate through a one-time photolithography process. Also, after the liquid crystal displaying portion and circuit element portion can be simultaneously produced by the same process order by using two transparent substrates having a large area, respective rows including a plurality of units for producing liquid crystal displays in a line are, respectively, cut and separated. After that, secondary cutting and separation are carried out, wherein a plurality of units for producing a liquid crystal display can be produced at one time, and productivity of the liquid crystal displays can be increased.
Thus, material costs are made lower than that of the COF, wherein the liquid crystal display according to the invention can be obtained at a low cost, and since the development costs of a liquid crystal display according to the invention are cheap, the invention can satisfactorily meet a request for custom displays in a small production lot.
Still further, since the LSI mounted portion (circuit substrate portion) is transparent, the electrode thereof is transparent, and the LSI is cemented to the transparent substrate by a binder, the connected state of the conductive lines of the LSI mounted portion can be visibly checked, wherein it is possible to check the conductive-connected portion (connection portion between the circuit substrate portion and liquid crystal portion) of the LSI mounted portion for which yield may be the most deteriorated during production, and a liquid crystal display having high reliability can be obtained.
Also, in the prior art shown in FIG. 12, not only is the circuit substrate 57 consisting of a polyimide resin film particularly expensive, but also the workability of mounting a hard LSI 56 onto the circuit substrate 57 made of soft polyimide resin film is difficult. However, according to the method of the invention, a hard. LSI 5 may be only mounted on a hard transparent substrate 3, wherein handling of the parts can be facilitated, a fully automated process is enabled, and the productivity thereof can be increased.